VIENNA — Nuclear talks between Iran and world powers pushed past their latest deadline Tuesday, as negotiators insisted that a deal could be reached by the end of the week but said they remain ready to walk away if agreement proves impossible.

“I believe we will, in the near term, either get this deal or find out we can’t,” a senior Obama administration official said. “On any given day, if we feel that we’re just not going to get there, that will be that.”

Negotiators hesitated to call their new goal of completing an agreement by Friday a “deadline.” But a State Department official said an interim accord that has paused and reversed some elements of Iran’s nuclear program since early last year would be extended at least until then.

Foreign ministers of U.S. negotiating partners — Britain, France, Germany, Russia and China — who arrived Monday in hopes of sealing a deal, left Vienna again late Tuesday, saying they would return later in the week.

Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif remained behind, continuing the grueling and nearly nonstop meetings that they and their aides have conducted for the past 11 days on what they have called the “endgame” of more than 18 months of negotiations.

Zarif said he had canceled plans to accompany Iranian President Hassan Rouhani to Russia for a summit Thursday of major emerging nations. “Unfortunately, I have to stay in Vienna for nuclear talks,” Zarif told reporters.

Negotiators were mostly tight-lipped on the remaining sticking points in any deal to lift international sanctions against Iran in exchange for long-term restrictions aimed at preventing Iran from being able to build nuclear weapons.

Iran has insisted that its nuclear activities are purely for peaceful energy and research purposes.

Iranian officials here, and Russian Foreign Minister Sergei Lavrov, said one of the most vexing remaining issues was whether the United Nations Security Council would lift prohibitions on sales of conventional weapons and ballistic missiles to Iran.